fix: consistent `std::int32_t` in AdaptiveGridTrackDensity #26119

Job	Run time
linux_ubuntu	15m 30s
linux_ubuntu_extra (ubuntu2204, 20)	15m 22s
macos	11m 11s
linux_ubuntu_extra (ubuntu2204_clang, 20)	54m 50s
linux_examples_test	13m 31s
linux_physmon	20m 20s
linux_physmon_perf_report	0s
	2h 10m 44s

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